1. Field of the Invention
The present invention relates to a battery pack.
2. Description of Related Art
A battery pack including plural secondary battery cells can be used repeatedly as a power source by supplying electric energy from outside the battery, that is, by storing electric energy inside the battery by recharging the battery when the residual capacity of the battery is reduced.
As a method of recharging the battery pack, there exists a dedicated charging station in a case of an electric car, and recently, there is a method of recharging the battery from an outlet at home. Other various power supply methods are known in addition to the above at the time of recharging the battery. Especially, in a case of a hybrid car, a generator is actuated by utilizing the power of an engine during running, and generated electricity is stored.
In recent years, a type of a car which can recharge the battery from an outlet at home when the car is stopped has appeared in a hybrid car. There is also a method of recharging the battery by regenerating heat generated at the time of applying a brake in the case of the car.
A related-art battery pack in which battery cells are housed in a metal case and both ends of the cells are connected to current collecting plates is known (for example, refer to Japanese Patent No. 4923314).
FIGS. 4A and 4B are views showing a related-art battery pack described in Japanese Patent No. 4923314.
In FIGS. 4A and 4B, battery cells 110 are housed in a metal block 120 in a state where directions of positive electrodes are aligned.
A positive-electrode current collecting plate 130 is welded to the positive electrode side of the battery cells 110, and a negative-electrode current collecting plate 123 is welded to the negative electrode side. A resin holder 140 is interposed between the positive electrode current collecting plate 130 and the battery cells 110, thereby performing insulation between positive electrodes and negative electrodes and preventing a short circuit. The positive-electrode current collecting plate 130 and the negative-electrode current collecting plate 123 are fixed to the resin holder 140 by screws 150a, 150b. As typified by the battery pack described in Japanese Patent No. 4923314, a battery pack using lithium-ion rechargeable batteries is normally constructed as a system by combining plural battery cells. In this case, the positive electrodes of respective battery cells are connected to one current collecting plate, the negative electrodes of respective battery cells are connected to one current collecting plate, and a widely used method for the connections is welding.
The battery pack including plural battery cells is difficult to be used as a battery pack when any one cell indicating an abnormal state exists due to some factors. For example, the above-noted state corresponds to cases where electrical characteristics are not satisfied due to the mixture of a battery cell which does not satisfy required characteristics or a welding failure between the positive electrodes/the negative electrodes of the battery cells and the current collection plate in manufacturing processes.
When excessive electric current flows into a particular cell due to a short circuit caused by a foreign object inside the cell or a welding defect with respect to the current collecting plate during the use of the battery pack, one cell can be remarkably deteriorated or the function of the battery can be lost.
In this case, the battery pack can be used again if only the battery cell indicating the abnormal state can be changed, or normal battery cells are collected from plural battery packs and newly combined. However, it is difficult to separate normal battery cells from the current collecting plate without impairing the shape or electrical characteristics when the battery cells and the current collection plates are welded as described in Japanese Patent No. 4923314.